Cellulosic pellicles coated with antisticking agent



i l l i l I 106. COMPOSITIONS,

COATING R PLASTIC.

Patented July 2, 1940 cxamme CELLULOSIC PELLICLES OOATED WITH ANTISTICKING AGENT John D. Pollard, Kenmore, N. Y., assignor E. I.

du Pont de Nemours & Company, Wilmingto Del., a corporation of Delaware No Drawing. Application February 2, 1938, Serial No. 188,319

Claims.

This invention relates to improvements in smooth, non-fibrous, non-porous sheets, films and pellicles and the method of making the same. More particularly, the invention relates to the production of cellulosic pellicles, especially water sensitive pellicles formed from aqueous alkaline cellulosic solutions, whereby to greatly enhance certain physical characteristics and consequently, their utility to manufacturer, converter and consumer. The invention will be described in terms of regenerated cellulose sheets and films although it is to be understood that this is illustrative and not limitative.

Regenerated cellulose, if manufactured in the pure form, is characterized by great brittleness and lack of flexibility. .Cellulose however, has a strong aflinity for water, and even in the absence of any other softening material will absorb a substantial amount of water from the surrounding atmosphere. If the surrounding atmosphere is of high relative humidity, such as around the water absorbed contributes sufficient softness so that only comparatively small amounts of additional softener are necessary to make the film commercially useful. In order, however, to make the film flexible and non-brittle at all humidities, a substantial amount of a relatively non-volatile hygroscopic softener, such as g l l h, is customarily 1mpregnated into the film. When this is done, the moisture absorbed-by the film at high relative humidities tends to make it more flexible than is actually necessary. However, this does no particular harm except for the fact that it very markedly increases the tendency of superimposed sheets to stick together, particularly when pressure, even though moderate, is applied. This tendency has been a problem affecting the commercial handling of the film for a great many years.

In order to overcome this difficulty, it has been proposed to apply to the surfaces of the film a thin, tenuous coating or sizingj, reducing the tendency of stacked sheets to stick together.

Heretofore, most of these sizes or antisticking aggnts have been only of limited effectiveness 'in preventing sticking and/or are not very receptive to water soluble glues customarily used in the fabrication of packages or the like and/or have a tendency, when applied in too large quantities, to cause haze or blush in the film.

It is therefore an object of this invention to produce thin, non-fibrous, substantially nonporous sheets and films having an improved resistance to sticking together, which have a satisfactory glue receptivity, and a minimum amount of haze or blush.

It is a furtherobject to produce such sheets or films having an improved resistance to sticking together in atmospheres of high relative humidity even when containing large quantities of a softening agent.

It is a still further object to produce sheets or films of regenerated cellulose or other water sensitive pellicles formed from aqueous alkaline cellulosic solutions which have an improved resistance to sticking together in atmospheres of high relative humidity even when containing large quantities of a softening agent.

It is a still further object to produce new sizin; materials for improving the resistance of non-fibrous cellulosic sheets and films to sticking together in atmospheres of high relative humidity even when containing large quantities of a softening agent.

Other objects will appear hereinafter.

The objects of this invention are accomplished by sizing such sheets or films with a thin, tenuous coating comprising a water-insoluble amide applied from aqueous colloidal solution or dispersion containing an emulsifying agent for said amide.

According to the preferred form of this invention, the sizing or antisticking agents are applied to transparent, regenerated cellulose sheets while such sheets are in the gel state. By the gel state is meant a pellicle containing a considerable quantity of water, for example, 30 to 40 .-parts of water per 10 parts of cellulose, and

which has never been dried substantially beyond the above-mentioned water content. Preferably this is accomplished by passing the regenerated cellulose in continuous form through a. bath containing the W t gether with the em a en in the desired concentration. m is most conveniently done just prior to the drying operation and at the same time as impregnation with a softener, such as glycerin. Before entering the drier, the excess antisticking agent, together with the excess softener solution, may be removed by suitable squeeze rollers, scraper rods, doctor knives or the like. The amount of antisticking agent which is applied is controlled by adjusting the concentration of the antisticking agent in the treating bath, or by varying the amount of excess removed. If it is desired to apply the antisticking agent separately, the pellicle may be treated with a softener bath, the

excess removed as indicated above and then the 66 solution or dispersion of the antisticking agent applied by dip rolls, sprays, or the like. The invention is also applicable to the production of film containing no softener, such softener free film being used for certain special purposes.

In general, the amides which are applicable in the practice of thmtion are those that are solid at ordinary temperatures and have a melting point preferably above about 60 C. Preferably only very minute quantities of such amides are applied to the transparent regenerated cellulose pellicle. Such substances, after drying of the pellicle, will usually and preferably amount to less than 2% of the product and may even amount to as little as a few hundredths per cent.

In the practice of this invention there may be used solid amides which are solid at all ordinary temperatures (e. g. 25 C.) and preferably having a melting point above 60 C., said amides being 20 re a ve y w e. Said amides belong to the class respresented by the following formula:

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 1'7 carbon atoms. R1 and B: may be hydrogen or a saturated aliphatic hydrocarbon radical containing 2 to 18 carbon atoms with or without hydroxyl groups. Of these, the most easily available and suitable are octadecyl amide, stea l stearamide, laur l lauramiae,

ydroxy steara'mi e, ethanol h droxy stearamide, ethano. stearamide an ethano aurami e. e 'amoun. of such solid ma erial 111 so ution necessary to form the desired concentration in the final product is customarily between 0.01% and 1%. and preferably between 0.20% and 0.5%. Other solid amides are also suitable, but those mentioned above are the most commercially available. The amidic substances of this invention, while giving excellent surface slip and other desirable surface conditions when present upon the surface of transparent film, offer certain difiiculties to a uniform and satisfactory application to the surface of said film. These materials are 1nsoluble, and, since they are relatively inert, it is not possible to form soluble derivatives, such as salts, to facilitate their dispersion in aqueous systems such as those required in the preferred method of application. Moreover, it is impractical, if not impossible to obtain satisfactory emulsions or dispersions by the use of colloid 55 mills or other physical methods of dispersion.

Since such sizing agents are generally a constituent of a softening bath containing, for instance, l cer 1 Miis general] culating systemJt is .highly des r e t at such 60 ma eria s as are added should remain in suspension for a long period of time and for a considerable range of conditions met with in the treatment and application of the bath. Such conditions include a wide range of temperature, 65 contact with different parts of circulating apparatus, stagnant periods in reservoirs, etc.

In carrying out the sizing treatment, it is preferable that the solution be so prepared, that the quantity be so controlled and that drying 70 be so carried out that the final product is substantially not inferior to similar unsized products, particularly in the retention of transpanency and brilliance and receptiveness to the usual aqueous adhesives. Furthermore, the product 75 should resist cohesion, such as caldng of stacked sheets when stored under pressure and/or exposed to atmospheres of high humidity, as much or more than similar unsized sheets even though the product may contain as much as twice the quantity of softening agent as the unsized prod- 5 uct. For this reason many restrictions are placed on the sizing or antisticking composition. For example, in order to get the best results it is necessary to emulsify the amide by means of a suitable emulsifying agent.

Although there are many substances which may serve as emulsifyin a ents for forming emulsions of the am'ides 0% the present invention, particularly desirable results have been obtained by the use of an emulsifying agent comprising sodium silicate and a saturated fatty acid, conaining from 12 to 18 car on a ms, such as for instance, stearic aci uc an emulsifying agent will not only produce highly desirable dispersions, but will enhance the surface slip produced by the sizing material. It is only necessary that the solids such as the amides and the acids be melted and mixed with the water, after which the sodium silicate is added with stirring. A highly stable emulsion results which may be added to an appropriate bath for treating the film as previously indicated. This is illustrated in Example 1. As another particularly efficient emulsifying agent for the amides of this invention may be mentioned triethanolamine stearate which may be formed s1 u y 2 ad ion to the amide of stearic acid and triethanolamine as illustrated in Examples 2, 3, and 4.

Example I 1.1 parts of the solid amide, such as octadecyl amide- (sometimes called s te;ar a m ige), an'H' I3 parts of stearic acid are melted and added to 56 parts of water and thoroughly mixed. 2.0 parts of sodium silicate solution comprising 28% S102, 8.5% NazO, and 63.5% H2O, are then added with stirring. The concentrated dispersion thus formed is then added at a temperature of 85-90 C. with stirring to an aqueous bath containing 7.5% glycerin to form a .4% colloidal dispersion of totm.

The following examples are illustrative of concentrated dispersions of solid amides which may be prepared by the use of stearic acid and triethanolamine. These concentrated dispersions may be added to aqueous baths containing glycerin in the same manner as outlined above in Example 1.

Example II Stearamide gra.ms Stearic acid do Triethanolamine do Water cc- Alcohol do Example III Lauramide grams stearic acid do Triethanolamine do Water cc Alcohol d0 I A regenerated cellulose film is passed through a bath of the type above exemplified, preferably 76 I06. COMPOSITIONS,

COATING OR PLASTIC.

while in the gel state, the excess liquid removed by means of squeeze rolls, and the film is then dried and wound up into rolls. The resulting film, when placed in stacks will not stick to adjacent films even when subjected to high relative humidity for an extended period of time.

As has been indicated above, celiulosic pellicles f the type described which are dense, non-fibrous and substantially impermeable possess a remarkably smooth surface. Customarily such pellicles are dried by passing them in a continuous manner over a series of drier rollers, and the surface of these rolls is usually smooth so that the surface of the pellicle will not be marred during its passage thereover. As the pellicle is dried, it tends to shrink in width, and with smooth rollers the shrinkage is more or less unrestricted in the case of the usual untreated pellicle so that considerable loss in width is experienced. It might be expected therefore that a pellicle treated in accordance with the present invention to improve the sticking resistance would present a still smoother surface to the drier rollers and would result in even greater shrinkage as the pellicle is dried. It has been found, however, and surprisingly so, that many of the sizing or other antisticking compositions within the scope of the invention are capable of preventing this shrinkage to such an extent as will result in substantially no greater loss in width than would be experienced if no sizing treatment were given.

The sized pellicles of the present invention, as above intimated, exhibit a high resistance to sticking to each other even when containing in excess of by weight of softeners, and when exposed to high relative humidities over extended periods of time. These pellicles have a good recaptivity to the usual aqueous adhesives, such as, for example, an adhesive containing dextrin, calcium chloride, and glycerin. Printing inks will adhere satisfactorily to the surface of the pellicles produced in accordance with the present invention.

It will be seen from the foregoing that in the preparation of the product it is necessary to overcome certain obstacles which are not encountered in any other product now known. Whereas stacks of transparent regenerated cellulose sheets are readily caked or stuck together by increases in moisture or pressure, paper, being porous, less hygroscopic and relatively rough in surface, exhibits no such action. Even the glassine papers which most nearly approach transparent regenerated cellulose film are free from caking or sticking. Cohering and gluing of transparent regenerated cellulose sheets differ widely from any such problem which has been encountered in the paper field. Even the densest of papers is sufficiently porous so that a wide variety of adhesives, for example, starch, casein, dextrln and gelatin agglutinants provide suitable adhesion. Plain transparent regenerated cellulose sheets, on the other hand, are smooth, non-fibrous and impervious to the usual colloidal agglutinant products and hence require specially compounded adhesives to secure proper adhesion of the smooth and substantially impermeable surface. Therefore, sizing or antisticking agents which would in no way afi'ect the gluing properties of glassine paper, for example, would so prevent the wetting and adhesion of an aqueous adhesive on the surface of transparent regenerated cellulose pellicles that no useful adhesion whatsoever would result. It thus becomes apparent that the sizing or antisticking agents which will improve LAuilllllbi the sticking resistance of regenerated cellulose pellicles and at the same time permit the pellicles to remain receptive to aqueous adhesives which are satisfactory for use with untreated pellicles constitutes an outstanding contribution to the art. Needless to say, there are many uses to which cellulosic pellicles of the type described might be put wherein the antisticking characteristic is of major import while the receptivity to aqueous adhesives is of little concern. In such cases, a pellicle having improved sticking resistance, regardless of its receptivity to aqueous adhesives, will be useful, and the production of such pellicles comes well within the scope of the present invention.

Likewise, the adhesion of printing inks to surfaces of transparent, regenerated cellulose pellicles is often greatly impaired except where the gluable compositions of the present invention are employed.

Certain treatments have been developed for imparting moistureproofness and/or waterproofness to transparent regenerated cellulose sheets. While these treatments may generally be applied to highly softened sheets to produce transparent, sticking resistant products, they invariably result in products which cannot be glued with com mercial aqueous adhesives. Furthermore, such processes require a second step, as of applying lacquers after the film has been dried and wound up. One very practical feature of the process of this invention is that it may be carried out at practically no increase in cost and without any alteration in the machine usually used for producing transparent regenerated cellulose sheets or in the method for subsequent handling by the manufacturer or converter or consumer.

Although this invention has been described in terms of sizing gel film, it may also be applied to film which has been dried and rewetted. However, this procedure is generally to be avoided since it necessitates an additional step in the manufacture, thus increasing the cost. It is also applicable to other smooth, non-fibrous, nonporous sheets and films which, because of their general nature or high content of softener, have a tendency to stick together, particularly water sensitive pellicles cast from aqueous or alkaline aqueous celiulosic solutions, including lowly substituted cellulose ethers, esters and ether-esters, such as glycol cellulose, methyl cellulose, ethyl cellulose, cellulose glycollic acid, and cellulose phthalic acid. I

Obviously many changes and modifications can be made in the above-described methods and products without departing from the nature and spirit of the invention. It is, therefore, to be understood that the invention is not to be limited except as set forth in the appended claims.

I claim:

1. Film cast from an aqueous, alkaline, cellulosic solution, said fllm having a size thereon, said size consisting of a water-insoluble amide which is solid at a temperature of C., the sized film being receptive to aqueous adhesives and permeable to moisture.

2. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially a water-insoluble compound having the formula;

. R, in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R: are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups, the sized film being receptive to aqueous adhesives and permeable to moisture.

3. Film cast from an aqueous, alkaline, cellulosic solution, said film sized with octadecyl amide.

4. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially an emulsion comprising a water-insoluble compound and an emulsifying agent for said compound, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R2 are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups, the sized film being receptive to aqueous adhesives and permeable to moisture.

5. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially an emulsion comprising octadecyl amide and an emulsifying agent for said amide.

6. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially an emulsion comprising a water-insoluble amide which is solid at a temperature of 25 0., sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms. 7. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially an emulsion comprising a water-insoluble compound, sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R; are members oi? the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups.

8. Film cast from an aqueous, alkaline, cellulosic solution, said film having a size thereon, said size comprising essentially an emulsion comprising octadecyl amide, sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms.

9. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline, cellulosic solution an emulsion consisting of water, a water-insoluble amide which is solid at a temperature of 25 C. and an emulsifying agent for said amide, and drying said film.

10. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline,

cellulosic solution an emulsion comprising essentially a water-insoluble compound and an emulsifying agent for said compound, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R2 are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups.

11. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline, cellulosic solution an emulsion comprising octadecyl amide and an emulsifying agent for said amide.

12. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline, cellulosic solution an emulsion comprising a Water-insoluble amide which is solid at a temperature of 25 0., sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms.

13. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline, cellulosic solution an emulsion comprising a water-insoluble compound, sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R2 are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups.

14. The process of making a transparent, nonfibrous, stick resistant pellicle which comprises applying to a film cast from an aqueous, alkaline, cellulosic solution an emulsion comprising octadecyl amide, sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms.

15. A sizing emulsion suitable for use on films cast from aqueous, alkaline, cellulosic solutions, said emulsion consisting of water, a water-insoluble amide which is solid at a temperature of 25 C. and an emulsifying agent for said amide.

16. A sizing emulsion suitable for use on films cast from aqueous, alkaline, cellulosic solutions, said emulsion comprising essentially a water-insoluble compound and an emulsifying agent for said compound, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R2 are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups.

COATiNG R PLASTIC.

1'7. A sizing emulsion suitable for use on films cast from aqueous, alkaline, cellulosic solutions, said emulsion comprising a water-insoluble amide which is solid at a temperature of C., sodium silicate, and a saturated fatty acid containing from 12 to 18 carbon atoms.

18. A sizing emulsion suitable for use on films cast from aqueous, alkaline, celluloslc solutions, said emulsion comprising a water-insoluble compound, sodium silicate, and saturated fatty acid containing from 12 to 18 carbon atoms, said compound having the formula;

in which R is a saturated aliphatic hydrocarbon radical containing 11 to 17 carbon atoms, and R1 and R2 are members of the group consisting of hydrogen, saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms and saturated aliphatic hydrocarbon radicals containing 2 to 18 carbon atoms with hydroxyl groups.

19. The process which comprises melting 1.1 parts of octadecyl amide and 1.3 parts of stearic acid, adding the melted mixture to 56 parts of water, thoroughly mizn'ng the resultant, adding with stirring 2 parts of sodium silicate solution analyzing 28% S102, 8.5% NaaO and 63.5% H20, adding, with stirring, suflicient of the concentrated dispersion thus obtained at a temperature of 85-90 C. to an aqueous bath containing 7.5% glycerin to form a .4% colloidal dispersion of total solids, passing a regenerated cellulose film in gel state through the resultant bath, removing the excess bath liquid and drying the resultin film.

20. A sizing emulsion adapted to prevent the sticking of super-imposed films cast from aqueous alkaline cellulosic solutions consisting of water, a water insoluble alkyl amide in which the number of carbon atoms in the alkyl group is not less than 7 and not more than 17 and an emulsifying agent for said amide.

21. An article of manufacture comprising a film cast from an aqueous alkaline cellulosic solution and a size thereon, the said size consisting of an alkyl amide in which the number of carbon atoms is not less than 11 and not more than 1'7.

22. A sizing emulsion adapted to prevent the sticking of superimposed films cast from aqueous alkaline cellulosic solutions consisting of octadecyl amide, sodium silicate, and stearic acid.

23. A sizing emulsion adapted to prevent the sticking of superimposed films cast from aqueous alkaline cellulosic solutions comprising essentially octadecyl amide, the emulsion having been prepared with the assistance of sodium silicate and a saturated fatty acid containing not less than 12 carbon atoms and not more than 18 carbon atoms.

24. An article of manufacture comprising a film cast from an aqueous alkaline cellulosic solution and a size thereon, the said size comprising essentially an alkyl amide from the group consisting of octadecyl amide, myristamide and lauramide. i

25. An article of manufacture comprising a regenerated cellulose film having a size thereon, the said size comprising essentially octadecyl amide.

JOHN D. POLLARD. 

